The present invention relates generally to disk drives, and more particularly, to disk drives having a transducer head which is separated from a storage medium by a fluid film, such as air, when the storage medium is moving at an operational rotational speed, wherein the storage medium has a reduced rotational speed in a low power mode.
Most disk drive data storage devices experience prolonged periods of data read/write inactivity. This is particularly true for disk drives that run continuously overnight or during holidays. Maintaining standby operations is a waste of energy especially where the power system of the disk drive is powered from a limited power source, such as batteries of a portable device, or where heat dissipation is a problem. As microcomputer based systems employing disk drives become ever-present in the work place and are often continuously operational, such systems must comply with standards requiring lower power consumption. Completely powering down the disk drive to reduce power consumption requires a relatively long wait time after the disk drive is powered back up for the disk drive to become ready to read or write data. Moreover, frequent power on and off cycles result in increased wear and possible high stiction events between the disk storage media and transducer head of the disk drive that reduce the useful life of the disk drive. Thus, during idle periods it is desirable to reduce power consumption while maintaining a near operational status of the disk drive.
During idle periods, principal power consumption in the disk drive is from the spindle motor maintaining the rotational speed of the disk media. Therefore, to conserve energy during idle periods, conventional power-saving techniques reduce spindle motor current which accordingly reduces the rotational speed of the disk media. However, reducing the rotational speed of the disk media can increase the risk of potentially damaging contact between the transducer heads and the disk media surface. Furthermore, a reduction in disk media rotational speed also typically disrupts the disk drive""s servo system, which otherwise maintains disk rotational speed at a near constant speed and provides information regarding the location of the transducer heads relative to the disk media.
To overcome these potential problems, conventional power saving techniques typically, prior to reducing disk rotational speed, either xe2x80x9cparkxe2x80x9d the transducer heads at an off-disk location or move the transducer heads to an above-disk location providing the maximum transducer-to-disk clearance. However, each xe2x80x9cparkingxe2x80x9d operation causes wear on the transducer assembly and slows initial post-idle seek times required to be ready to read or write data. Furthermore, repeated and prolonged operation with the transducer heads above a single disk track ultimately results in burnishing of both the transducer heads and the disk surface.
Thus, there is a need for a disk drive system having a low power mode of operation wherein the rotational speed of the disk media is reduced without compromising the mechanical integrity of the disk media or the transducer head.
One aspect of the present invention provides a disk drive and a method of performing a power-saving idle operation in a disk drive. The disk drive includes at least one disk having a disk surface and at least one transducer head for writing and/or reading data from the disk surface. A spindle motor is coupled to the disk to rotate the disk. A voice coil motor is coupled to the transducer head to provide a radial velocity component to the transducer head to radially position the transducer head relative to the disk surface. A programmable controller performs the power-saving idle operation which controls the spindle motor to reduce spindle motor current to thereby slow disk rotation. The power-saving idle operation also controls the voice coil motor to vary voice coil motor current to thereby continuously move the transducer head radially relative to the disk surface in a repeating sweeping pattern between a selected inner disk diameter and a selected outer disk diameter. The varying voice coil motor current is a function of the transducer head""s radial position in relation to the disk surface.
In one embodiment, power-saving idle operation controls the voice coil motor to vary the voice coil motor current to thereby vary the radial velocity component of the transducer head. In one embodiment, the power-save idle operation controls the voice coil motor to vary the radial velocity component of the transducer head based on a radial velocity idle sweep profile representing a relationship between the radial velocity component of the transducer head and its radial location relative to the disk surface that optimizes head-disk interaction (HDI) when the disk is rotating at a given reduced rotational speed. In one embodiment, the programmable controller includes memory storing at least one look-up table containing optimal radial velocity idle sweep profiles. In one embodiment, the power-save idle operation estimates and corrects achieved radial velocity component of the transducer head versus voice coil motor current.
In one embodiment, the programmable controller determines the transducer head""s radial position in relation to the disk surface based on sensing when the transducer head reaches the selected inner disk diameter and the selected outer disk diameter. For example, in one embodiment, the programmable controller senses when the transducer head reaches the selected inner disk diameter based on reaching an inner diameter crash stop and senses when the transducer head reaches the selected outer disk diameter based on a read signal from the transducer head disappearing when the transducer head reaches the selected outer disk diameter.
In one embodiment, the selected inner disk diameter is an inner most disk diameter and the selected outer disk diameter is an outer most disk diameter. In another embodiment, the selected inner and outer disk diameters are selected to prevent the transducer head from traversing a disk area where vital data is stored. In another embodiment, the selected inner and outer disk diameters are selected to prevent the transducer head from traversing disk areas where a flying height of the transducer head from the disk surface is lowest.
In one embodiment, the power-save idle operation controls the spindle motor to slow disk rotation to a first reduced disk rotational speed based on not receiving a command within a first time period. In one embodiment, the power-save idle operation controls the spindle motor to further slow disk rotation to a second reduced disk rotational speed based on not receiving a command within a second time period.
The power-saving idle operation of the disk drive according to the present invention can reduce the potential for damaging transducer head-disk interference and also can reduce the mechanical wear on the transducer heads during power-saving idle periods by maintaining the transducer heads in a constant sweeping motion relative to the disk surface and by reducing and/or eliminating transducer head traversing of selected disk diameters. The power-saving idle technique of the present invention can also retrieve data more quickly when returning to seek mode from idle mode than other conventional power saving idle techniques. Moreover, the power-saving idle technique of the present invention can be practiced in existing disk drives without modification to the existing servo system.